How do I load an mp4 video with multiple audio tracks into blender?
Blender does not currently support the importing of multiple audio tracks that are encoded into video containers. It will typically import the first track, though I'm not certain. I recommend that you use a program like Davinci Resolve which is free to use and is much better suited for video editing and has a faster viewport for video editing. I was once in a similar situation like you with multiple tracks of audio when using OBS.